Conventionally multi-stage reciprocating compressors are known. For example, JP 2016-113907 A discloses a compressor including a crank shaft, a first compressing portion configured to compress gas, and a second compressing portion configured to further compress the gas which has been compressed by the first compressing portion. The first compressing portion has first to third compression chambers. The second compressing portion has fourth and fifth compression chambers. The compressor is provided so that a first pressurizing portion linearly reciprocates via a first reciprocation converter and a second pressurizing portion linearly reciprocates via a second reciprocation converter under a rotation of the crank shaft. The gas is thereby compressed in the five compression chambers.
With regard to the compressor disclosed in JP 2016-113907 A, a passage interconnecting the first and second compression chambers requires, for example, a portion (volume) in which gas discharged from the first compression chamber is temporarily stored before the gas discharged from the first compression chamber is suctioned into the second compression chamber because the suction and discharge of the gas is performed simultaneously in the first and second compression chambers. The same may be said for a passage interconnecting the second and third compression chambers as well as a passage interconnecting the fourth and fifth compression chambers.
As described above, during a period from discharge of gas from a compression chamber at a low pressure side to suction of gas into another compression chamber at a high pressure side, the gas temporarily stays in the connecting portion configured to interconnect the compression chambers. The staying gas has a pressure higher than a suction pressure of the compression chamber at the high pressure side, which causes power loss. Adding a volume to the connecting portion in order to avoid the increase in pressure in the connecting portion results in a larger number of parts constituting the connecting portion, which in turn raises a risk of gas leakage. In some cases, such a volume may not be provided because of spatial restrictions.